The present invention relates to an apparatus for measuring the ratio of alcohol contained in mixed fuel, wherein the ratio of alcohol contained in fuel for use in a car engine, for example, is measured and used to achieve effective engine control in relation to the air/fuel ratio and the like.
Mixed fuels in which alcohol is mixed with gasoline or light oil have been used as car fuel, for example. In the case of using mixed fuels, it is necessary to accurately known the ratio of alcohol to gasoline or alcohol to light oil in order for the engine to be controlled in the most suitable way to achieve an efficient air/fuel ratio.
As an engine fuel, alcohol is different from gasoline in that it needs a different air/fuel ratio, different anti-knock components and so on. When alcohol-mixed fuel is used, but when electronic control of the engine is carried out according to an engine control program which uses only gasoline as fuel, the control output and vehicle driveability are lowered. This results in a violation of the exhaust gas pollution regulations. In the case of using mixed fuel, therefore, it is necessary to control the amount of fuel injected, the timing of the ignition and the like according to the ratio of alcohol contained in the mixed fuel. This is the reason why the ratio of alcohol contained in fuel must be accurately and easily detected and measured when mixed fuel is used.
The following are ways to measure the ratio of alcohol contained in mixed fuel. The first way is to use electrostatic capacity. A pair of electrodes are opposed to each other in a fuel pipe with a space between them in through which mixed fuel is passed. More specifically, the electrostatic capacity between the electrodes is measured based on the fact that the electrostatic capacity between the paired electrodes thus arranged will change depending upon the ratio of alcohol mixed into the fuel. The second way is to grasp, as impedance, the change in the electrostatic capacity between paired electrodes which have been arranged similar to those in the first method. The third is to arrange matter in the pipe, and then to detect and measure the ratio of alcohol contained, by measuring the change of in the matter's property caused by the interaction between the matter and alcohol particles.
When an alcohol ratio measuring device is to be provided according to any of these measures, it is necessary to arrange electrodes in the pipe through which fuel is supplied to the engine, thereby making that portion of the pipe where the electrodes are attached more complicated. It is necessary, particularly in this case, to prevent fuel leakage from that part of the pipe where the electrodes are attached. That part of the pipe must be made completely oil-tight and strong.